(a) Field of the Invention
The present invention relates to a vibration reducing system and method at key-off that control ignition of a preselected cylinder to occur last before engine shutoff.
(b) Description of the Related Art
When a vehicle ignition key is turned off, vibrations occur, particularly in diesel engines since the compression ratio is high and combustion force is very large. These vibrations are unpleasant and may deteriorate marketability.
One method for reducing these vibrations is to stop the engine as soon as possible. Fuel injection is stopped, and a throttle valve is simultaneously closed to cause a cylinder to be in a vacuum state and hinder movement of a piston.
A mechanical throttle actuator, including a vacuum source, a vacuum modulator, and a diaphragm; and an electrical throttle actuator, including a DC motor, are both provided. These throttle actuators are expensive and serve only to reduce vibrations at key-off.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.